It is well known to fabricate containers by process of blow molding, wherein a blank parison or “preform” is positioned within the cavity of a mold and injected with a pressurized gas, usually air, causing it to inflate and assume the contours of the mold cavity. The contours of the mold are configured in the shape of a container, such that when the preform is inflated within the mold it is thereby formed into a container.
One common variant of this is the stretch blow molding process, wherein the preform is mechanically stretched along a longitudinal axis while being inflated. Preforms used in a stretch blow molding process have a closed end, such that the preform generally resembles a test tube with a closed end and a mouth at an open end. These preforms are also generally provided with flanges, threads, etc. at the mouth, to permit the attachment of a closure device to the mouth of the finished container.
During the stretch blow molding process, a stretching rod or similar device is inserted into the mouth of the preform and advanced, pushing at the preform from within and stretching it along its longitudinal axis as the air is injected. The mouth of the preform remains substantially un-deformed, while the body of the preform is stretched and expanded to match the contours of the mold in which it has been placed.
Stretch blow molding is thus particularly well-suited for the fabrication of elongated containers, namely those used for packaging mineral water and other beverages. While this document is concerned with the use of the stretch blow molding process for the fabrication of beverage containers, it should be understood that the principles discussed herein may be equally applicable to the fabrication of containers for other substances and applications.
Apparatuses for stretch blow molding comprise, at the least, the aforementioned mold (optimally provided in two or more mobile segments to facilitate extraction of the finished container) and an injection head for injecting pressurized gas into the cavity of the preform, and possibly inserting and removing the stretch rod.
The apparatus may have a single chamber, but more frequently is provided in a multiple-chamber form with multiple molds. Using multiple molds will improve the output of the container fabrication process, which is greatly advantageous in commercial container fabrication and bottling operations.
In high-volume stretch blow molding implementations, these molds are conventionally disposed upon the circumference of a large, rotating wheel. The mold is opened when the wheel reaches a certain angular position, the preform is inserted and the mold closed around it, and the injection head injects the gas into the preform as the wheel rotates, such that by the time the wheel returns to the initial angular position the container within the mold segment is completely formed and removed for cleaning, filling, and sealing.
By utilizing a wheel with multiple molds and having multiple injection heads acting on multiple preforms disposed within the molds, containers may be produced continuously and at a very high rate of production relative to a single-mold apparatus. When operated in combination with a filling and sealing line, tens of thousands of filled and sealed containers may be so produced. Generally speaking, the higher the number of mold cavities disposed on the wheel, the higher the rate at which the containers may be fabricated.
One particular embodiment of this principle is found in the document EP1226017, which describes a molding apparatus wherein there is a plurality of mold segments each configured so as to form a mold cavity with the corresponding face of an adjacent mold segment. These mold segments are not disposed upon the edge of a wheel, but at the ends of radial supports resembling spokes, so as to revolve about a common axis.
The radial supports may be further adapted with means to permit the radial displacement of the mold segments, both in an absolute sense and relative to each other, and may be further adapted so as to permit an axial displacement of a mold segment. By way of these displacement means, each of the mold cavities between the mold segments are opened and closed during the operation of the molding apparatus.
However, the apparatuses known in the prior art require a considerable amount of floor space when implemented in a container fabricating and filling operation. Along with the wheel-shaped forming apparatus, one need supply at least an apparatus for filling the containers with the liquid product, as well as transport belts or carriers for moving the preforms and containers between them. This limits the production that any one facility may realize for a given floor space and may make an increase in production prohibitively expensive.
Furthermore, the apparatuses known in the prior art require a great deal of energy to operate. Specifically, it is desirable to clamp the mold segments together during the molding operation to prevent the formation of a mark in the surface of the container along the parting line where the mold segments meet. One must therefore furnish means of clamping the mold segments together with great force. This requires a great deal of energy and entails the addition of still more machinery, further increasing the space required for the molding apparatus and the complexity of its construction and operation.
It is therefore an object of this invention to provide a molding apparatus which is more space-efficient than the ones known in the art, and which consumes less energy during the production of containers.